The chemical structures of the major urinary metabolites of three compounds either tested or on test in the NTP have been determined. The major metabolite of allylisothiocyanate in the rat was found to be a mercapturic acid, N-acetyl-S-(N-allylthiocarbamoyl)-L-cysteine. The major metabolites of benzyl acetate in the mouse and rat were the glycine conjugate, hippuric acid, and the mercapturic acid, S-benzyl-N-acetyl-L-cysteine. The major metabolites of 2,4-dinitroaniline have been tentatively identified as the sulfate conjugate, N-(2,4-dinitrophenyl) hydroxylamine-O-sulfonic acid and the corresponding hydroxylamine.